Phosphorus-nitrogen compounds



atent 3,0i8,l65 Patented Jan. 23, 1.962

of imidodiphosphoric acid such as tetrasodium imidodi- The production ofthe other alkali salts such as lithium, rubidium and cesium is also apart of this invention.

Tetrasodium imidodiphosphate has been made by older methods, but theseprocesses have been characterized by the production of a very impureproduct, and also a very low yield. It has now been found that theproduction of these very useful salts as well as other alkali salts ofimidodiphosphoric acid may be improved by conducting the reaction in thepresence of a flux comprising a molten salt. The reactant which isemployed as the raw material in this process is a dialkaliphosphoramidate such as the sodium or potassium phosphoramidate. Thedisodium phosphoramidate has the formula It has been found that whenthis compound is heated to a temperature in the range of from 200 C. to250 C., a preferred temperature range being from 215 C. to 230 C. in thepresence of a molten salt as a medium or flux, the production of thedesired salt of imidodiphosphoric acid, such as tetrasodiumimidodiphosphate is greatly improved. The proportion of the flux is notcritical, and it has been found that wide variations such as allproportions above 10% by weight of flux relative to the weight ofdisodium phosphoramidate may be used. A preferred range is 10 to 1,000%by weight. The prior art methods of producing this salt without the aidof a flux required a reaction in the solid state which results only in avery slow reaction between particles of the solid material. It has nowbeen found that the use of a flux makes it possible for the reaction tobe more readily conducted and with a greatly superior reaction rate. Incarrying out the prior art method, it was found that 24 hours reactiontime gave a 6% yield of product accompanied by seven times its weight ofimpurities. In comparison, the present process in the same period gave a35% yield of product accompanied by one fourth its weight of impurities.

The molten medium or flux which is employed in the present process iscomposed of the salts which are liquid in the range of from 150 C. to300 C. A preferred flux for this purpose is potassium formate, whileother desirable fluxes are sodium phenoxide, potassium phenoxide, andmixtures thereof in all proportions. An example of another organic saltwhich is of utility in this relationship is cesium formate.

The following examples illustrate spechic embodiments of the presentinvention:

EXAMPLE 1 This example shows the preparation of tetrasodiumimidodiphosphate from disodium phosphoramidate with potassium formate asthe flux. One hundred grams of disodium phosphoramidate hexahydrate wasdehydrated under vacuum, raising the temperature to 90 C. over a sixhour period, held at 110 C. for 24 hours and finally at 125 C. for 2hours. The dry solids were ground in a dry-box and mixed with twice asmuch powdered potassium formate. (This had been prepared by heatingcommercial potassium formate to 220 C. and adding about one grampotassium hydroxide for every 500 grams potassium formate so that a 2%solution in water would indicate a pH of 11.3 with a pH meter; oncooling the cake was crushed to a powder.) The mixture was heated in aglass vessel under vacuum as follows: one hour at 160 C., three hours at200 C., and twenty four hours at 230 C. It was cooled and dissolved in250 ml. water. On chilling the solution to 5 C. and adding an equalvolume of denatured ethanol, the product precipitated as needles, andwas filtered oif from the major proportion of the impurities whichremained in solution. The crystals were Washed and dried. The yield was40 grams of purity of the decahydrate.

In order to obtain the anhydrous salt, the decahydrate was dried under 3mm. pressure at 50-60" C. The identity of the product was determined bynuclear magnetic resonance measurements.

EXAMPLE 2 This experiment shows a condensation with potassium phenoxidepresent. Forty grams of disodium phosphoramidate hexahydrate, Na PO NH-6H O, was dehydrated under oil pump vacuum (1 mm), with P 0 in aside-bulb, by the following schedule: 65, 4 hrs.; 2 hrs; 16 hrs; 2 hrs.The product was cooled, crushed to a fine powder in a dry-box, and mixedintimately with 50 g. finely crushed potassium phenoxide. The solidswere heated under oil pump vacuum, with KOH in a side-bulb, by thefollowing schedule: 1 hr.; 200, 3 hrs; 230, 24 hrs. On cooling, thesolids, which had sintered together, were broken up and dissolved in 250ml. water and precipitated with ethanol. On reprecipitating from water,with 4 g. NaOH present, by slowly adding excess ethanol, needles wereobtained. Yield, 32 g. (89%). Purity, by NMR, was about 95%, with smallamounts of phosphoramidate, orthophosphate and pyrophosphate present.

It has been found that detergent formulations of unusual efiiciency,particularly liquid detergent concentrates may be formulated with thealkali imidodiphosphates and in particular the potassiumimidodiphosphate as an essential constituent. Both wet and dry detergentcompositions may be formulated with the alkali imidodiphosphate. Thesaid alkali imidodiphosphates may be present accordingly as dry salts inconventional dry detergent formulations and also in high concentrationliquid detergent concentrates. It has been found that development ofautomatic detergent apparatus such as dishwashing machines, clotheswashing machines, etc. requires the use of a very high concentration ofthe active components when such liquid concentrates are to be fed byautomatic proportioning machines into the washing apparatus. It istherefore a particular advantage of the present alkali imidodiphosphatesthat they are characterized by unusually high solubility in Water sothat they may be present as components of the active solutions in highconcentration.

The alkali imidodiphosphates have been found to act as sequestrants andalso as alkaline builders in the detergent formulation. The said alkaliimidodiphosphates have been found therefore to suppress theprecipitation of calcium soaps, i.e., the formation of soap scum andalso to provide a buffered or controlled proportion of alkali whichenables the conventional active organic components such as sodiumdodecyl benzene sulfonate to operate at maximum efiiciency.

EXAMPLE 3 A representative detergent formulation based upon the use oftetrasodium imidodiphosphate was prepared with the following components:

Percent Sodium salt of dodecyl benzene sulfonic acid 35 Sodium carbonateSodium sulfate 13.5 Tetrasodium imidodiphosphate 40 Sodium metasilicate5 Carboxyrnethylcellulose 1.5

The above formulation was tested as a detergent composition and found tobe effective in removing various types of soil.

EXAMPLE 4 Certain of the compositions of the present invention were alsotested for calcium sequestration properties.

The procedure is based on the fact that the oxalate ion will notprecipitate calcium from the calcium-sequestrant complex in alkalinesolution (over pH The sequestering agent is titrated with a standardcalcium solution in the presence of oxalate indicator. When thesequestering agent is completely complexed, a slight excess of calciumwill precipitate as calcium oxalate indicating that the end point hasbeen reached. If the sequestering solution is too dilute, the end pointis delayed.

Determination of sequestering efiectiveness (1) A sample (5-20 grams) ofthe sequestering agent is weighed accurately to 0.01 g. and made up to500 ml. with distilled water in a volumetric flask.

(2) Pipette 3100 ml. aliquots of this solution into 3 250 ml. beakers.

(3) Pipette 10 ml. of 5.0% ammonium oxalate indicator into each aliquot.

(4) The pH value of the aliquot is determined with the Beckman pH meter.The pH value is adjusted to exactly 11.0 with dilute sodium hydroxide.All aliquots must be adjusted to the same pH value.

(5) Fill a 10 ml. burette with the standard 0.50 M calcium chloridesolution. Titrate the aliquots with calcium chloride solution until afaint permanent turbidity is observed, which is the end point. The endpoint can be more easily detected if the beaker is placed on a blackbackground. Record mls. of standard calcium chloride used to the nearest0.01 ml. It is suggested that the first aliquot be titrated to give theapproximate end point, and then the other 2 aliquots titrated carefullyto give the exact end point.

(6) A blank is run using distilled Water and the indicator. The blank issubtracted from the sample titrations.

The sequestering action of tetrasodium imidodiphosphate is shown by thefollowing data, determined by the above procedure:

Comparison of solubility and calcium sequestration It is seen from theabove data that per g. saturated solution in water at 25 0, sodiumimidodiphosphate will sequester 2.5 times as much calcium as sodiumpyrophosphate.

EXAMPLE 5 The above detergent formulation was also prepared withtetrapotassium imidodiphosphate; similar tests were also made todetermine the solubility and calcium sequestration ability which againproved to be superior to conventional pyrophosphate.

What is claimed is:

1. Process for the preparation of tetrasodium imidodiphosphate whichcomprises heating disodiurn phosphoramidate in the presence of a moltensalt selected from the group consisting of potassium formate, cesiumformate, sodium phenoxide, potassium phenoxide, and mixtures thereof ata temperature in the range of from 200 C. to 250 C. the said salt beingpresent in the proportion of at least 10% by weight relative to theweight of the said disodium phosphoramidate, and thereafter recoveringthe tetrasodium imidodiphosphate from the reaction mixture.

2. Process for the preparation of tetrasodium imidodiphosphate whichcomprises heating disodium phosphorarnidate in the presence of a moltensalt selected from the group consisting of potassium formate, cesiumformate, sodium phenoxide, potassium phenoxide, and mixtures thereof ata temperature in the range of from 200 C. to 250 C., the said salt beingpresent in the proportion of from 10% to 1,000% by weight relative tothe Weight of the said disodium phosphoramidate, and thereafterrecovering the tetrasodium imidodiphosphate from the reaction mixture.

3. Process for the preparation of tetrasodium imidodiphosphate whichcomprises heating disodium phosphoramidate in the presence of potassiumphenoxide as a fiux at a temperature in the range of from 200 C. to 250C. the said flux being present in the proportion of at least 10% byweight relative to the weight of the said disodium phosphoramidate, andthereafter recovering the tetrasodium imidodiphosphate from the reactionmixture.

4. Process for the preparation of tetrasodium imidodiphosphate whichcomprises heating disodium phosphoramidate in the presence of potassiumformate as a flux at a temperature in the range of from 200 C. to 250 C.the said flux being present in the proportion of at least 10% by Weightrelative to the weight of the said disodium phosphoramidate, andthereafter recovering the tetrasodium imidodiphosphate from the reactionmixture.

References Cited in the file of this patent UNITED STATES PATENTS2,503,381 Eichwald Apr. 11, 1950 2,897,052 Teuber July 28, 19592,906,601 Koster et al Sept. 29, 1959 2,932,616 Blake Apr. 12, 1960

1. PROCESS FOR THE PREPARATION OF TETRASODIUM IMIDODIPHOSPHATE WHICHCOMPRISES HEATING DISODIUM PHOSPHORAMIDATE IN THE PRESENCE OF A MOLTENSALT SELECTED FROM THE GROUP CONSISTING OF POTASSIUM FORMATE, CESIUMFORMATE, SODIUM PHENOXIDE, POTASSIUM PHENOXIDE, AND MIXTURES THEREOF ATA TEMPERATURE IN THE RANGE OF FROM 200* C. TO 250* C. THE SAID SALTBEING PRESENT IN THE PROPORTION OF AT LEAST 10% BY WEIGHT RELATIVE TOTHE WEIGHT OF THE SAID DISODIUM PHOSPHORAMIDATE, AND THEREAFTERRECOVERING A TETRASODIUM IMIDODIPHOSPHATE FROM THE REACTION MIXTURE.